In the extraction of oil from earth boreholes, the oil may be extracted from a single location or "zone" within the well, or oil may be extracted from multiple zones within the well. To aid the well operator in maximizing the depletion of the oil within the earth formation, it is desirable to know a variety of information, such as temperature, static pressure, dynamic and acoustic pressure, flow rate, resistivity, etc., about the fluid being produced from each zone within the well.
Coiled tubing is known to be useful for a variety of oil field exploration, testing and/or production related operations. Metal coiled tubing is utilized in oil and/or gas wells by being reeled into and out of a production tubing string.
One use of coiled tubing is for production logging. For example, coiled tubing is used to deliver various sensors for making measurements of the production fluid within the well, e.g., pressure, temperature, resistivity, etc. Sensors are positioned at the end of the coiled tubing, and then the coiled tubing is driven into the well to position the sensor at a desired depth within the well. Alternatively, various types of well tools and sensors are delivered down the coiled tubing after it is positioned within the well. The measurements made using various sensors are performed as single point measurements corresponding to the position of the end of the coiled tubing. The sensor location may be varied by repositioning the coiled tubing for making measurements at multiple locations within a well. While single point measurements provide the well operator with valuable production information, information that is much more valuable could be obtained with simultaneous measurement of multiple parameters at multiple locations within a well, preferably while the well is flowing.
Electrical sensors currently used in oil wells are limited for several reasons. The on-board electronics of such sensors must operate in a very hostile environment, which includes high temperature, high vibration and high levels of external hydrostatic pressure. However, electronics, with its inherent complexity, are prone to many different modes of failure. Such failures have traditionally caused a less than acceptable level of reliability. Additionally, electrical transmissions are subject to electrical noises in some production operations.
Therefore, a reliable method is needed for accurately measuring parameters of a harsh environment, such as a borehole. Additionally, a method and system is needed for measuring multiple parameters at multiple locations within the harsh environment.